Potassium iodide based gold etchant from Transene will etch Cu and not
affect Ni.  I'm not sure what it will do to Ag.

>  2008/5/29, Sardar Bilal :
>  >
>  > Hello folks !
>  >
>  > I have a question related to metal etching. I want to etch my Cu seed layer
>  > (100 nm by sputtering). Its a bit tricky since I also have about 100 nm of
>  > Ni and 100 nm of Ag on my wafer which I want to keep. I have tried 10%
>  > nitric acid at room temperature, but it etches Cu and Ni at almost the same
>  > rate, though silver is not etched significantly. I have also tested 10% HCl
>  > and i observed the loss of adhesion of some Ni structures (strange!) and Cu
>  > was not etched significantly. When the sample was taken out of HCl, it
>  > oxidized and Cu color changed to purple shades. I would appreciate if
>  > someone can recommend some wet etchants that can selectively etch Cu and
>  > have low etch rate for Ni and Ag.